This chemosensor device has direct application in assisting law enforcement in identifying fish that have been illegally caught via the practice of cyanide fishing by detecting thiocyanate as an analyte in sea water. This would also have application in characterizing the efficacy of antifouling coating of boats and ships, by detecting the diffusion of thiocyanate to surrounding water. Thiocyanate is typically an additive to motor oil to prevent corrosion in off-shore drilling apparatus and in marine engines—sensitive thiocyanate detection in seawater could aid in maintenance of equipment in salt-water environments. Most thiocyanate that is detected natively in marine or terrestrial environments is generated biotically as a metabolite in response to cyanide in the environment. For example, a sensitive sensor for thiocyanate may have application to future NASA missions to detect life in aqueous environments within our solar system. Detection of thiocyanate would be a suggestive indicator for microbial life.
There are a number of problems typically associated with accurately identifying fish that have been caught by cyanide fishing. Currently for law enforcement to determine that a fish has been caught via cyanide fishing, they must sacrifice some sample fish for blood testing in a laboratory, or by a newer method, possibly detect thiocyanate in the water around the fish via a modified high-pressure liquid chromatography technique that is laboratory based with a detection limit of 3.2 ppb in seawater after preconcentrating the sample.
There is a need for a hand-portable chemosensor device that can detect thiocyanate in seawater directly without treatment down to under 2 ppb; use of the chemosensory electrode in a laboratory environment for cyclic voltammetry on seawater to below 1 ppb. Rapid, on-site analysis in this fashion is highly desirable and would provide increased forensic capability for law enforcement by entities such as the U.S. Fisheries and Wildlife Service. The use of electrodes in laboratory analysis extends the capability of sensitive detection significantly.
There have been some attempts in the prior art to address these needs. The most direct comparison in the literature or amongst patents is a method using polyethyleneglycol (PEG) modified optical fibers in line with HPLC separation to detect thiocyanate in seawater down with-a detection limit of 3.2 ppb (Silva, I7.I.B., et. Al.; J Environmental Monitoring, 2011, 13, 1811). Another HPLC method touted for its sensitivity in recent literature describes HPLC with ion detection, used to characterize naturally occurring thiocyanate in cow's milk in the ppm regime (Phonchai, A., et. Al.; Analytical Methods, 2016, 8, 4983). There are air quality sensors that detect volatile organic compounds (VOCs) that are hand portable and capable of detecting methyl thiocyanate at 0.1-5000 ppm (http://www.ionscience.com/products/tigerlt).
There are numerous prior art patents that are directed to a “thiocyanate chemosensor”. However, the vast majority of those prior art patents have thiocyanate as a component to aid in detection of metal ions. There is a subset of patents for the detection of thiocyanate in saliva related to cigarette smoking, and HPLC methods that are patented for thiocyanate detection in food. In both cases of smoking and food, the dangerous limits for thiocyanate are on the order of ppm, rather than ppb, so the sensitivity in these methods is not comparable.
Further, the use of metalloporphyrins for ion sensing, including detection of thiocyanate are well known (Zhang, Y; Wang, H.; Yang, R. H.; Sensors, 2007, 7, 410), with the emphasis on colorimetric and/or fluorescent detection of ions is also well known in the art. In Zhang and coworkers paper, their detection limit was 6.00×10−4 M (equivalent to 34.8 ppm) which is much less sensitive than the Silva HPLC/optical fiber method. In addition, halide ions (chloride Cl—, bromide Br—, iodide I—) are potential interferents for colorimetric/fluorescent detection which makes the method unsuitable for marine environments.
Despite the attempts in the prior art, there is still a need for a device, method and system that detects thiocyanate in seawater with the halide ions present; a device that is hand-portable and which offers detection limits to 1-2 ppb which at least twice as sensitive as the nearest known device in the current state of the art.